Create collapsible debug panel; start on GoonWidget improvements.
Move debug panel to the bottom (so it's top-most widget).
Change GoonWidget to have its origin at the top left corner.

Previously, the dropdown arrow was to the left of the origin.
Do the same for ChannelExpeWidget.
Improve type under caret detection.

Now it prints types for both uses and definitions.
Use setupInternals3 in NewGoonWidget for editing ability of root entry.